1. Field of the Invention
The invention relates to optical microcavities based on two dimensional photonic crystals, which are optimized for maximum Q factor and minimum load volume. These cavities can also be used for strong coupling between the cavity field and an atom trapped within a hole of the photonic crystals.
2. Description of the Prior Art
Various passive and active optical devices can be constructed by introducing point or line defects into a periodic array of holes perforating an optically thin semiconductor slab. Point or line defects into a periodic array of holes has previously been used in making a semiconductor (InGaAsP) laser emitting at xcex=1.55 xcexcm, and for demonstrating silicon optical waveguides with sharp bends. In these structures, light is confined laterally by means of distributed Bragg reflection and vertically by total internal reflection. The advantage of this approach lies in facilitating the integration of many optical components on a single chip.
Microcavity formation via alteration of the refractive index of a single defect hole in a hexagonal photonic crystal has been previously analyzed theoretically. In that analysis, the radius of the defect was equal to that of the unperturbed holes in the photonic crystals, but its refractive index was tuned between one and the refractive index of the slab. It was predicted that, in the described structure, dipole defect modes can be excited with quality factors as high as 30000. However, that analysis was in fact incorrect for reasons described below. Q factors of the structures analyzed in the prior art were in fact of the order of 2000 at a maximum.
The invention is an optical apparatus or optical microcavity comprising an array of holes or regions of optical discontinuity in a photonic crystal, and a defect in the array of holes created by elongation of the holes in the array in a predetermined direction thereby defining in the array of holes in the photonic crystal an asymmetrical optical cavity with a Q factor in excess of 2000 and typically in excess of 30,000. The holes are generally air filled, but they may also be filled with material which is distinct from the material of the photonic crystal, namely an optically nonlinear organic material.
In the illustrated embodiment the array of holes in the photonic crystal is an hexagonal array, but any geometric array may be equally substituted. The optical cavity which created by the invention may be used in a laser, a waveguide or a filter among other any other photonic device now known or later devised.
In the illustrated embodiment the asymmetrical optical cavity which is created by elongation of a single row of holes in the array in a predetermined direction. This elongation allows tuning of frequency and Q factor of a cavity. The optical cavity is arranged and configured to support modes having maximum electric (E) field intensity in the air region. This is useful for cavity QED experiments, or tunable filters having photonic crystal holes filled with electro-optic polymers. For the purpose of cavity QED experiments the optical cavity is characterized by a critical atom number, N0, and a photon number, m0, less than 1.
Again in one embodiment the array of holes has a central hole with a radius reduced relative to other ones of the holes in the array, and a row of holes including the central hole have their radii elongated in a defined direction. The neighboring ones of the holes are characterized by a distance between their respective centers and the array of holes has a central hole with a radius reduced to r2 relative to other ones of the holes in the array. Selected neighboring holes to the central hole have their radii reduced to r1 relative to other ones of the holes in the regular array and moved by rxe2x88x92r1 away from the central hole in a direction defined by a line connecting centers of the central hole and the neighboring holes to preserve the distance between the neighboring holes and holes neighboring them in turn along a defined direction. A row of holes including the central hole have their radii elongated in the defined direction. The reduction of radius r2 and r1 movement by rxe2x88x92r1 and elongation in the defined direction are chosen so that the microcavity created thereby is tuned.
From yet another viewpoint the defect is arranged and configured in the array to maximize microcavity mode quality factor Q and to minimize mode volume. Vmode.
In another view the defect is arranged and configured in the array to strongly couple cavity field with a single gas phase atom.
The spaces within the holes are termed as hole regions. The defect is arranged and configured in the array to provide a maximum of E-field intensity in a hole region. The hole region may be an air filled or filled with a material different from the material of the photonic crystal.
In other embodiments the defect is arranged and configured in the array to provide a maximum of E-field intensity in a region within the photonic crystal.
The invention is also defined as a method of fabricating an apparatus with the above characterizing features using an analogous combination of steps.
While the method has been described for the sake of grammatical fluidity as steps, it is to be expressly understood that the claims are not to be construed as limited in any way by the construction of xe2x80x9cmeansxe2x80x9d or xe2x80x9cstepsxe2x80x9d limitations under 35 USC 112, but to be accorded the full scope of the meaning and equivalents of the definition provided by the claims. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals.